Current and voltage references are building blocks used in many electronic devices. With increasing numbers of portable electronic devices and with increasing demand for reduced power consumption, demand for low-power, high precision reference circuitry to provide stable reference currents, reference voltages, or both, has increased.
Programmable references based on floating-gate technology gained popularity during the last decade. Thus, programmable floating-gate devices can be used to provide adjustable voltages or currents in a continuous range of values. A floating-gate transistor, for example, can be programmed to produce a reference voltage by tunneling a controlled amount of electric charge onto the floating-gate, which charge is stored on the capacitor associated with the floating-gate. The threshold voltages of such programmed floating-gate transistors are stable or relatively constant for a wide range of supply voltages and temperatures, providing means for implementing a voltage reference or a current reference.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items.